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| author | KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> | 2009-09-23 15:56:33 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-09-24 07:20:58 -0700 |
| commit | 261fb61a8bf6d3bd964ae6f1e6af49585d30db51 (patch) | |
| tree | 417cebd2e18bc2457b5b09d8359ad71ba6afd56d /mm/memcontrol.c | |
| parent | 4b3bde4c983de36c59e6c1a24701f6fe816f9f55 (diff) | |
| download | linux-261fb61a8bf6d3bd964ae6f1e6af49585d30db51.tar.gz linux-261fb61a8bf6d3bd964ae6f1e6af49585d30db51.tar.bz2 linux-261fb61a8bf6d3bd964ae6f1e6af49585d30db51.zip | |
memcg: add comments explaining memory barriers
Add comments for the reason of smp_wmb() in mem_cgroup_commit_charge().
[akpm@linux-foundation.org: coding-style fixes]
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
| -rw-r--r-- | mm/memcontrol.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b0757660663f..eb9571815f0c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1134,6 +1134,13 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem, } pc->mem_cgroup = mem; + /* + * We access a page_cgroup asynchronously without lock_page_cgroup(). + * Especially when a page_cgroup is taken from a page, pc->mem_cgroup + * is accessed after testing USED bit. To make pc->mem_cgroup visible + * before USED bit, we need memory barrier here. + * See mem_cgroup_add_lru_list(), etc. + */ smp_wmb(); switch (ctype) { case MEM_CGROUP_CHARGE_TYPE_CACHE: |